1. Field of the Invention
The invention relates to the identification of liquid crystal display panels, and more particularly, to determining the type of the liquid crystal display panel based on the frequency of an oscillating signal generated in the liquid crystal display panel.
2. Description of the Related Art
In recent years, with the increasing popularity of portable computer systems, the variety of liquid crystal displays (LCDs) available to the user has increased dramatically. An LCD panel comprises an array of display elements known as pixels. Each pixel on the LCD panel can be one of two states, on or off. In its "on" state, the pixel allows light to be transmitted, whereas in its "off" state, the pixel prevents light from passing through. The pixels are activated by electronic drivers located in the LCD panel. The electronic drivers are controlled by a video controller located in the base unit of the portable computer system. The LCD panel is typically divided into an upper and lower half, with the upper half being connected to a set of upper column drivers and the lower half being connected to a set of lower column drivers.
Since driving a liquid crystal at direct current (DC) triggers an electrode reaction inside the liquid cell that results in a rapid deterioration of the display quality of the liquid cell, an alternating current (AC) driving method must be utilized. Two AC driving methods exist: static and multiplex. In the static driving method, each display pixel must be driven by a dedicated liquid crystal driver circuit, thereby making the static method unsuitable for a liquid display with a large number of display pixels. In the multiplex method, each row of pixels in the LCD panel is driven by a corresponding common driver, while each column in the upper half of the panel and each column in the lower half of the panel are driven by a corresponding upper column driver and a corresponding lower column driver, respectively. The waveforms of the signals generated by the common and column drivers define which pixels are activated. Since each pixel in the LCD panel is defined by a common signal and an upper or lower column signal, depending on which half of the LCD panel the pixel is located, the combination of the two multiplexed AC signals determine whether the accessed pixel is activated. The video controller provides the control and data signals to the drivers to manipulate the pixels on the LCD panel to produce the desired image.
Different types of LCD panels can be utilized in a portable computer system. As each type of LCD panel has different characteristics, the video controller must be initialized differently for the different types of panels. The video controller is initialized during the computer's Power On Self Test (POST) procedure. For proper initialization of the video controller, the computer must be informed of the type of LCD panel. Parameters associated with the different types of LCD panels are stored in a Video Read Only Memory (Video ROM). During POST, the computer first identifies the LCD panel type, and then accesses the appropriate location in the Video ROM to obtain the power on parameters corresponding to the LCD panel. The computer utilizes those parameters to properly initialize the video controller. In prior systems, the LCD panel type was indicated by providing a number of additional pins from the LCD panel to the portable computer system. Thus, by encoding the additional pins with certain values, the computer is able to determine the type of LCD panel being used. A disadvantage of this method is the number of extra wires that are required to be routed from the LCD panel to the base unit of the portable computer system. Further, as the number of panels that can be used with a given video controller changes, so must the number of pins, quickly reaching pin and wiring problems, as noted above, and cost, logistical and standardization problems with LCD panel vendors.
Thus, a method of determining the LCD panel type is desired that does not require unnecessary pins or additional components to be provided by the LCD panel.